iS8 THE PHYSIOLOGY OF PLANTS 



containing sap within t\ie berries becomes more concen- 

 trated, i.e., more sweet. The process of respiration, during 

 which a portion of the organic acids is oxidised to carbonic 

 acid, is not interfered with. by twisting the stalks. 



The greatest retardation of currents is produced by breakingr 

 the branches. If a shoot which has already formed its secon- 

 dary wood is broken over the blade of a knife, a splintered 

 wound is formed. The tip of the shoot is connected with the 

 base by a certain amount of bast and cortex and a very small 

 amount of wood. It dries up more rapidly the more woody 

 the region in which the break occurred. If the shoot is soft, 

 the wood is not splintered, and the drooping end of the shoot 

 very soon raises its tip and begins to bend upwards, but grows 

 very slowly indeed. 



(c.) notching. 



The fruit-grower is often compelled, so as to obtain trees of 

 a regular shape, to force a certain bud to develop without being 

 able to alter the position or form of branch to which it belongs. 

 In such cases, he has to resort to notching, i.e., to remove a 

 narrow sickle-shaped mass of cortex and young wood on one 

 side of the branch immediately above the bud. By so doing, 

 the upward current of water on this side of the branch is 

 diminished above the bud, while the latter, being more abun- 

 dantly supplied, will grow out very rapidly. If the notch is 

 made below the bud, the vascular bundles which supply the 

 leaf are usually severed, as they leave the woody cylinder of 

 the stem a good way below the leaf and run in the cortex for 

 a considerable way. The notch below the leaf stops the plastic 

 materials from passing downwards, and they accumulate chiefly 

 in the form of starch in all the parenchymatous cells in the 

 neighbourhood of the bud. This storage of food material is 

 considerable, as the woody cylinder is interrupted opposite the 

 bud, and a parenchymatous bridge reaches from the pith right 

 through the wood to the bud. The tissues surrounding the 

 bud thus become laden with food material at the same time 

 as the water supply diminishes. Such conditions are very 

 conducive to the formation of flowering buds. If a shoot is 



